Method for coating a golf ball with a dry-on-line clear polyurethane composition, and golf balls comprising such a coating

ABSTRACT

An improved clear polyurethane coating for a golf ball comprises a coating that dries on-line at elevated temperatures in 10 minutes and without assistance of a plural machine; a method for coating golf balls with the fast-drying coating system. The coating system provides improved flight characteristics to the golf balls.

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] This invention relates generally to golf balls and golf ballcoatings. More particularly, the present invention relates to golf ballshaving an improved polyurethane clear top coating that dries on-linewithout assistance of a plural machine, and to a method of coating agolf ball with a dry-on-line clear polyurethane. The coating system ofthis invention is particularly suitable for golf balls having a covercomprising an ionomer resin.

[0003] (2) Description of Related Art

[0004] A golf ball is generally classified into one of three types: agolf ball having a balata or urethane cover; a golf ball with a covermainly composed of an ionomer resin; and an integrally molded typeone-piece golf ball. All three of these golf balls are normally treatedin order to impart a white appearance thereto, making the golf ballsmore visible against green grass.

[0005] Golf balls can also be classified according to the method oftheir assembly as either a “three-piece,” a “two-piece” or a “one-piece”construction. The assembly of a golf ball generally involves molding acover around a solid or wound core. Golf balls with wound cores aretypically referred to as “three piece balls ” because they consist ofthree basic components: (1) a solid or liquid-filled center; (2) rubberwindings around the center; and (3) the cover.

[0006] Similarly, solid cores are referred to as having a “two piece”construction, since they consist solely of a solid core and a cover. Athird type of ball, known as a “one-piece” ball is also known in theart. As the name suggests, one-piece balls are solid balls ofhomogeneous construction made by any conventional molding methodsuitable for the purpose.

[0007] The composition of the golf ball cover has proven to be a factorin overall golf ball performance. Historically, three-piece balls hadcovers made of balata. Balata is a natural resin, essentially made up oftranspolyisoprene, and obtained from trees in South and Central America.Urethane covers are made from diisocyanates and polyols. Both a golfball having a balata or urethane cover and an integrally molded typeone-piece golf ball are coated with a paint containing a large amount ofwhite pigment.

[0008] The majority of modern golf balls use a two-piece or three-piececonstruction with covers made of an ionomer resin such as Surlyn®, aproduct of E.I. DuPont de Nemours Company, Incorporated. An ionomericresin is a polymer with covalent bonds between the elements of thechain, and ionic bonds between the chains. The Surlyn® covers are morecut-resistant than the balata covers.

[0009] In the case of a golf ball with a cover mainly composed of anionomer resin, the ionomer resin itself is transparent, and the whitepigment can also be formulated in the ionomer resin itself. Therefore, awhite appearance can sometimes be obtained by only providing a clearlayer without using the white paint.

[0010] There is a need for an improved clear polyurethane coating thatwill adhere well after weathering and that will resist abrasion. Goodadhesion of the polyurethane coating after weathering and resistance ofthe coating to abrasion are particularly important for driving rangeballs, often referred to as “range balls.” Because range balls are usedin all kinds of weather, over and over again for many years, they need atough and durable outer coating.

[0011] The durability and mechanical strength of an outer coating dependprimarily on the chemical structure of the coating, the mechanicalnature of the coating, and the thickness of the coating. The chemicalbonds in polyurethane are very strong. However the mechanical strengthof the coating depends largely on the presence of an optimal length ofurethane chain and an optimal density of crosslinkages. Two factorscontrol chain length and density of crosslinkages. One such factor isthe ratio of polyols and isocyanates used. The other factor is curingtime. Generally, a longer curing time tends to provide better filmmechanical properties of a urethane coating. Because mechanical strengthis particularly important in range ball coatings, prior art polyurethanecoatings used in the manufacture of range balls generally requireapproximately a 16 hour baking process in order to attain a durableurethane coating.

[0012] The durability of the urethane coating also depends on thethickness of the coating. Conventional practice is to either build up athick coating of urethane through multiple spray applications oflow-solid coatings or to apply a single layer of high solids coating.From a productivity standpoint, a single pass spray with high solids ismore economical. However, a high-solid, single-pass spray presentstechnical difficulties. One disadvantage of a conventional single-passspray process is that the material to be sprayed is very viscous andtherefore difficult to spray. Another disadvantage of a conventionalsingle-pass spray is that the thick layer produced dries slowly andtends to sag, causing a non-uniform thickness of coat. The resultantball is not uniformly spherical, and therefore exhibits poor flyingperformance.

[0013] Typical paints used to coat golf balls, including urethane golfballs, comprise two component polyurethane coatings, which have goodimpact resistance. One of the problems associated with conventional twocomponent polyurethane coatings is that they dry slowly. In order tospeed up drying, a plural machine is usually used.

[0014] Because of the slow drying nature of conventional polyurethanecoatings, the golf ball painting process requires many steps. In theconventional process for clear-coating a golf ball, the surface-preparedballs are first mechanically loaded onto a stamping machine that printsa logo or stamp on the balls. The balls are then continuously loadedonto spindles that carry the balls and travel along with a moving chainto pass by spray guns that apply a clear polyurethane top-coating to theballs. The chain then moves wet, painted balls through a heated oven topre-cure the coating. When they reach the end of the oven, the paintedballs are usually still not dry, and have to be manually unloaded fromspindles on the moving chain onto holding racks. The holding racks withthe balls are then placed into another heated oven to bake for another16 hours or longer at 100 degrees Fahrenheit in order to completely curethe coating before further processing or handling. Due to theslow-drying nature of a conventional clear coat polyurethane system, allthese steps, especially the 16 hour baking process, are necessary.

[0015] The conventional painting process has many drawbacks. First,manually loading wet balls from spindles on a moving chain on to holdingracks is very labor intensive and often results in damage or destructionof the surface of the balls. Due to human error, many well-painted ballsare often accidentally dropped off from spindles on a moving chain lineor off holding racks. The dropped balls are unusable and representsubstantial annual capital loss.

[0016] Secondly, there is a substantial labor cost to unload cured ballsfrom the racks into collecting hoppers for further processing. Thirdly,oven baking for 16 hours is time-consuming and consumes a substantialamount of energy. The ovens are large and require a large amount offloor space, which is also costly. The number of steps reducesproductivity substantially.

[0017] In addition, an inevitable, substantial problem is that unloadingwet balls off spindles onto loading racks often leaves balls withscratches or pin marks because the balls with wet paint have to betouched by another device. These scratches or marks are major causes ofquality control rejection for surface defects.

[0018] An even greater problem is that the heating of the balls for therequired drying time in the ovens deteriorates the rubber thread woundinside urethane balls. The performance of urethane balls dependssubstantially on the elasticity of the rubber thread wound inside theballs. The rubber thread windings have been analogized to an “engine” ofa wound ball. The deterioration by heat is due to the associated loss ofelasticity of rubber thread wound inside wound balls, and the resultingloss of performance.

[0019] Fast drying of the applied coating and long “pot life” of theurethane coating materials are both properties desired by paintersworking with urethane coatings. However, the fast drying and long potlife are properties that contradict each other. That is, the fasterdrying a formula is, generally the shorter the pot life is. Tocompromise, common practice in the industry is to use a so-called“plural component machine” or simply “plural machine” which mixescomponent A with component B containing a catalyst just before thecoating reaches the spray gun. This approach satisfies the painter'sneed to have a long pot life because components A and B are separateduntil the coating material reaches the spray gun. However, the pluralmachine is very expensive and one machine can serve only one paint line.If a shop has many paint lines, the capital investment is substantial.

[0020] For the foregoing reasons, there is a need for an improved clearpolyurethane coating for golf balls which can be applied in a singlespray, and which will dry quickly on-line without requiring oven-bakingand for a method for coating a golf ball with the improved, fast-drying,single spray polyurethane.

SUMMARY OF THE INVENTION

[0021] The present invention satisfies these needs with a clearpolyurethane coating for golf balls that dries on-line in approximately10 minutes without assistance of any plural machine, a coating that canbe applied in a single spray, that dries without sagging and that istough and durable, and with a method for coating golf balls thatcomprises using the coating composition and the coating system of theinvention.

[0022] Accordingly, the main object of the invention is to provide animproved clear polyurethane coating for golf balls that dries quicklyon-line, and a method for applying the improved coating.

[0023] A further object of the invention is to provide a fast-drying,clear polyurethane coating that can be applied in a single spray, isuniform in thickness, and imparts a shiny, smooth surface to golf balls.

[0024] Another object of the invention is to provide a fast-drying,clear polyurethane coating and a method for applying the coating thatproduce golf balls that are free of surface defects caused by wet ballsbeing touched by another device.

[0025] Another object of the invention is to provide a fast-drying,clear polyurethane coating that has good impact resistance and that issuitable to paint golf balls having ionomeric resin covers.

[0026] Another object of the invention is to provide a simpleformulation using a catalyst system that causes the coating to dry in aperiod of approximately 10 minutes and yet has good pot life and aconstant viscosity over the course of that pot life.

[0027] Yet a further object of the invention is to eliminate the needfor manually loading and unloading wet balls from spindles on a movingchain onto holding racks. By eliminating the need for manual loading andunloading, labor cost is reduced and the number of balls dropped anddamaged during handling is substantially reduced.

[0028] Another object of the invention is to eliminate the need for asecond oven-baking of wet-coated balls before further handling orprocessing. By eliminating the need for the second oven-baking, which inthe conventional method is carried out at a high temperature for 16hours, energy and floor space costs are significantly reduced and lossof performance of balls due to heat deterioration of interior rubberwindings is eliminated.

[0029] Another object of the invention is to provide an improved coatingsystem and method for coating golf balls that allow the coated balls tobe collected into containers directly from the painting line to befurther processed.

[0030] The foregoing and other objects of the invention have beenattained by providing a clear polyurethane coating for golf balls and acoating system that uses a drying accelerator which is part of thepresent invention. The drying accelerator substantially shortens thedrying time of the clear polyurethane coating. In addition, thecombination of catalysts used in the drying accelerator results in aviscosity that is more constant than that provided by a single catalystused in conventional systems. In conventional single catalyst systemsthere is a need to continually adjust the focus and air pressure of thespray guns due to rapidly changing viscosity.

[0031] The accelerator is comprised of two metal catalysts which have asynergistic effect on the drying of the polyurethane coating. It iscritical that both catalysts are used together, because if only one ofthe catalysts is used, the effect on drying time is substantially less.One of the catalysts comprises a chelated zirconium complex, availablecommercially as K-Kat 4205. The other catalyst, which works in synergismwith the zirconium catalyst is dibutyl tin di-laurate (DBTDL),commercially available as Metacure T-12. This combination imparts novelfast drying characteristics to the coating so that it dries on-line in aperiod of 10 minutes at temperatures of 170 to 180° F., yet hasreasonable pot life. The pot life is over 2 hours. This desirablebalance between fast drying characteristics and adequate pot lifesatisfies a long felt need in the industry, and would not be obtained byusing either of the catalysts separately.

[0032] The coating system also uses a surfactant to improve flowproperties of the coating material to be sprayed and to impart a shiny,smooth surface to the coated balls. This is important in golf ballcoatings because of the dimples on the surface of golf balls. If thecoating material to be sprayed on the balls has poor flowcharacteristics, the coating material will flood the dimples. The resultwill be uneven coating of the dimples. Because the dimples control theoverall flying performance of the balls, the uneven coating willadversely affect the flying performance of the balls. In this invention,a fluorosurfactant containing fluoroaliphatic polymeric esters in ethylacetate is used. The fluorosurfactant is commercially available asFluorad-431. Other surfactants would also work. Fluorad-431 ispreferred.

[0033] The paint system in this invention comprises a polyurethanecoating mixture, a two-component drying accelerator, and a surfactant.The unique drying accelerator and the surfactant were briefly describedabove. The polyurethane coating system is a conventional systemcomprising polyols, isocyanates, and solvents. The coating system ofthis invention, including the unique drying accelerator and thefluorosurfactant, provides a coating with good impact resistance, goodadhesion, flexibility, abrasion resistance, and toughness. These arenecessary characteristics of a coating system for golf balls, especiallyfor range balls. The system would be extremely slow-drying but for theunique two-component catalyst of the invention.

[0034] Thus the dry-on-line clear polyurethane coating for golf ballsand the golf ball coating method of the present invention provide asubstantially faster manufacturing process with much less heat exposureand a much greater percentage of golf balls produced without surfacedefects than in conventional golf ball coating systems. The result is asubstantial capital savings for the manufacturer and better performingballs due to less heat exposure in the coating process than inconventional systems. The painted golf balls produced in accordance withthis invention have significantly improved flying accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS.

[0035]FIG. 1 depicts a side elevation view of an embodiment of aschematic procedure for spraying golf balls with a Dry-On-Line ClearPolyurethane Composition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] At the outset the invention is described in its broadest overallaspects with a more detailed description following. The fast-dryingproperty of the paint system in this invention revolutionizes the wholepainting process into so-called dry-on-line. The present invention is aclear polyurethane coating system suitable for golf balls that drieson-line in a period of approximately 10 minutes under elevatedtemperature. Thus the painted balls can be dried on-line andmechanically transferred for further processing.

[0037] The method of this invention is performed as follows: Golf ballshaving a pigment such as white, yellow, or any other color mixed intothe golf ball cover are provided. For proper coating adhesion, thesurfaces of the balls are prepared by conventional methods, includingremoval of dirt and grease from the surface. In addition, the surfacesare “roughened” to increase surface area. The surface-prepared balls aremechanically loaded onto a stamping machine by which logos or stamps areprinted.

[0038] As shown in FIG. 1, the golf balls 10 a, 10 b, 10 c are loadedonto spindles 12 a, 12 b, 12 c, on a chain 14. The chain is moved by adrive system 16. The chain moves and carries the balls past a first setof spray guns 5 a, 5 b, that apply one coat of a conventional primerpaint to the balls. The primer paint comprises aziridine and anacrylic-urethane emulsion in water and other solvents. The chain movesthe balls into a first oven 6 where they are heated for about one to twominutes. The clear coating is applied immediately after the balls exitthe first oven. To apply the clear coating, the balls are carried by thechain past a second set of spray guns 18 a, 18 b. The balls 10 a, 10 b,10 c are sprayed with the clear polyurethane coating composition of thisinvention, and are moved along with the chain 14 into a heated oven 20.The chain travels in the oven 20 for a period of 10 to 15 minutes. Whenthe balls exit the oven after the 10 to 15 minute period, they aresufficiently dry to allow them to be mechanically knocked off directlyfrom spindles into collecting hoppers for further processing.

[0039] Thus, the coating system of this invention eliminates the stepsof manually loading wet, clear-coated balls; it eliminates 16 hours ofdrying time for the clear coat in a second oven; the need for a secondoven; and manually unloading cured balls into collecting hoppers.Furthermore, the dry-on-line process reduces quality rejection due toreduction in the number of balls with surface defects. The dry-on-lineprocess also maintains wound ball performance as designed because theprocess requires significantly less exposure to high heat thanconventional systems. Flight performance is also improved because ofeven-coating of the dimples resulting from the single-spray, high solid,low viscosity, fast-drying nature of the coating system of thisinvention.

[0040] The coating system in this invention comprises a polyurethaneclear coating mixture, a drying accelerator and a surfactant. Thecoating mixture that has a component of polyester polyols, ofisocyanates, and of solvents is supplied by Technical CoatingLaboratory, Inc., hereinafter referred to as “TCL,” in Avon, Conn. Thepolyurethane clear coating mixture is a clear base, commerciallyavailable as TCL 6249, comprising polyester polyols.

[0041] The ingredients of TCL 6249 include the following: ComponentWeight percent (approximate) Propylene glycol monomethyl 2 ether acetateXylene 1 N-butyl acetate 14 Ethyl acetate 16 Toluene 26 Cyclohexanone<0.5% Mineral spirits <0.5% Ethyl benzene <0.5% Non-volatiles 40.9

[0042] The clear base, TCL 6249, is mixed with the activator,commercially available as TCL 6263, comprising a blend of aliphatic andaromatic isocyanates.

[0043] The ingredients of TCL 6263 include the following: ComponentWeight Percent (approximate) Hexamethylene diisocyanate 1 Xylene 11N-butyl acetate 17 Toluene 8 Non-volatiles 64.1

[0044] The fluorosurfactant used in this invention, as previouslystated, contains fluoroaliphatic polymeric esters in ethyl acetate, andis commercially available as Fluorad-431.

[0045] The ingredients of Fluorad-431 include the following: ComponentWeight percent (approximate) Potassium fluoroalkyl carboxylate(C8) 40.0to 44.0 Water 32.0 2-Butoxyethanol 14.0 Ethyl alcohol  4.0 Potassiumfluoroalkyl carboxylate(C6) 1.0 to 5.0 Potassium fluoroalkylcarboxylate(C4) 1.0 to 5.0 Potassium fluoroalkyl carboxylate(C7) 1.0 to3.0 Potassium fluoroalkyl carboxylate(C5) 0.1 to 1.0

[0046] It is known that reactions of polyols with isocyanates formingpolyurethane linkage follow a nucleophilic reaction mechanism. Thereaction starts with a lone pair of electrons of oxygen in a hydroxygroup of polyols first attacking a carbonyl carbon of an isocyanategroup. The reaction speed will be greatly increased if any dissociationof hydrogen in a hydroxy group of polyols occurs since it empowersnucleophilic attack of oxygen due to increase of its electron density.

[0047] It is known that chelated zirconium such as K-Kat 4205 catalyzesthe curing of 2-component urethane coatings. It is also known thatdibutyl tin dilaurate (DBTDL) catalyzes the curing of polyurethane.However, the invention is directed to the combining of the twocatalysts, chelated zirconium and DBTDL, which the inventors discoveredhas a dramatic, synergistic effect on both curing time and theuniformity of coating and on the flying accuracy of a golf ball coatedwith the coating system of the invention.

[0048] As described previously, one of the catalysts comprises achelated zirconium complex, available commercially from King Industry asK-Kat 4205. The amount of K-Kat 4205 used in the present invention is1.2% on resin solid. If it were the only catalyst present in the coatingmixture, the Zirconium complex in K-Kat 4205 is believed to act as aLewis acid interacting with the hydrogen in a hydroxy group of a polyol.Thus, the nucleophilic attacking power of the oxygen in a hydroxy groupis greatly increased. As a result of the foregoing mechanism, the dryingof the polyurethane coating speeds up.

[0049] In order to provide a coating system which dries quickly on-line,it is critical that the polyurethane coating mixture includes a dryingaccelerator comprising two catalysts, a chelated zirconium complex anddibutyl tin dilaurate, which act in synergism with one another togreatly speed drying time. The mechanism for the synergism of the twocatalysts is unknown.

[0050] The following examples are illustrative for mixing procedure andapplication conditions of the coating system of the invention. Theexamples are provided for illustration but are not to be considered aslimiting.

EXAMPLE 1

[0051] Preparation of Catalyst Solution

[0052] For optimal results, the catalyst solution should be freshlyprepared. Into a container, add 10.0 grams of K-Kat 4205 and 0.3 gramsMetacure T-12. Stir until the two catalysts are well mixed, forming“Mixture 1.”

[0053] To prepare the catalyst solution, into a second container, add4.7 grams of the Mixture 1. Then add the following into the secondcontainer: 10.0 grams of FC-431, 32.0 grams ofparachlorobenzotrifluoride (PCBTF), and 32.0 grams of acetone. PCBTF iscommercially available as Oxsol-100, supplied by Oxychem. Mix theingredients present in the second container well. The catalyst solutionin the second container is ready to use as soon as it is well-mixed. Thetotal amount of the two component catalyst system is 78.7 grams. Thecatalyst solution should be kept covered as long as possible to minimizeloss of solvent by evaporation.

EXAMPLE 2

[0054] Preparation of Urethane Clear Coat Ingredients Code Solid % w/wAmount Clear base TCL 6249 40.90 550.0 grams Activator TCL 6263 64.10290.0 grams Catalyst solution 0.00  78.7 grams Total 918.7 grams

[0055] Example 2 illustrates the preparation of a clear coating systemwhich is used to coat golf balls, particularly range balls. Theingredients in the above table are mixed according to the followingprocedure.

[0056] At room temperature, the following materials are added to acontainer: 550.0 grams of clear base TCL 6249, 290.0 grams of activatorTCL 6263 and 78.7 grams of catalyst solution from Example 1. Thecontainer is put on a shaker to shake for 5 minutes. The clear coatingmixture is ready to spray golf balls.

[0057] In the above table for Example 2, the critical ratio of coatingcomponents is 550.0 grams of TCL 6249 to 290.0 grams of TCL 6263. Thepreferred range is plus or minus 10% from the critical ratio. Thecatalyst will work with any ratio of polyols and isocyanates.

EXAMPLE 3

[0058] Method of Applying a Clear Urethane Coating Mixture

[0059] Provide a freshly-prepared catalyst mixture prepared according toExample 1, and a urethane clear coat mixture prepared according toExample 2. Provide golf balls having a pigment such as white, yellow, orany other color mixed into the golf ball cover. Prepare the surface ofthe golf balls by removing dirt and grease. Roughen the surface of thegolf balls. Mechanically load the surface-prepared balls onto a stampingmachine by which logos or stamps are printed. Apply one coat of aconventional primer paint to the golf balls. This is done on-line, priorto the application of clear coat. As shown in FIG. 1, load the golfballs 10 a, 10 b, 10 c onto spindles 12 a, 12 b, 12 c on a chain 14.Connect the chain to a drive system 16 which moves the chain and carriesthe balls past a first set of spray guns 5 a, 5 b that apply one coat ofa conventional primer paint to the balls. Move the balls on-line into afirst oven 6 and allow them to be heated for about one to two minutes.When the balls exit the oven continue to move them past a second set ofspray guns 18 a, 18 b to be sprayed with clear coating while the ballsare still warm. Adjust the spray guns and chain speed to control thetotal weight of wet clear paint on a ball to between 200.0 and 210.0 mg.Adjust the chain speed of the painting line to 23.0 ft./min. (equivalentto painting 130 balls per minute).

[0060] The chain 14 moves and carries the balls 10 a, 10 b, 10 c pastspray guns 18 a, 18 b. The balls 10 a, 10 b, 10 c are sprayed with theclear polyurethane coating composition of this invention, and are movedalong with the chain 14 into a heated oven 20. The oven temperature isat 180° Fahrenheit. Allow the chain to travel in the oven 20 for aperiod of 10 to 15 minutes. When the balls exit the oven after the 10 to15 minute period, they are sufficiently dry to allow them to bemechanically knocked off directly from spindles into collecting hoppersfor further processing.

[0061] In this example, only one coat of polyurethane coating isapplied. The polyurethane coating is “high solids,” containing more than40% solids, but is applied in a single-pass spray. This is unlikeconventional single-pass spray coating systems, in which the high solidspray is too viscous for even coating. The viscosity of the high solidspray of the present invention is sufficiently low to make sprayingeasy. The clear coating is uniformly thick and the coated ball exhibitsexcellent flying characteristics.

[0062] Contrary to the “plural component machine” approach, theinvention provides a balance between drying speed and pot life ofurethane coatings. The composition of the invention dries in a period of10 minutes at a temperature of about 180° Fahrenheit, yet still has apot life of over 2 hours. This balance not only meets a fast dryingrequirement, but also offers reasonable pot life to painters. Coatingproperties of the invention are excellent.

[0063] This polyurethane coating has good adhesion, flexibility,abrasion resistance and toughness. However, without the criticalcombination of catalysts to which the present invention is directed, thecoating would dry slowly and require all the steps of conventionalsystems described previously.

[0064] While the present invention has been described in connection withpreferred embodiments thereof, it will be apparent to those skilled inthe art that many changes and modifications may be made withoutdeparting from the true spirit and scope of the present invention.Accordingly, it is intended by the appended claims to cover all suchchanges and modifications as come within the true spirit and scope ofthe invention.

What is claimed is:
 1. A golf ball, said golf ball having on its outersurface a clear polyurethane coating that is formed from a mixturecomprising a surfactant, a base, and a drying accelerator furthercomprising at least two metal catalysts.
 2. The golf ball of claim 1wherein the drying accelerator comprises a catalyst containingzirconium.
 3. The golf ball of claim 1 wherein the drying acceleratorcomprises a catalyst containing dibutyl tin dilaurate.
 4. A compositionsuitable for coating a golf ball with a clear polyurethane coatingcomprising a surfactant, a base, and a drying accelerator furthercomprising at least two metal catalysts.
 5. A composition according toclaim 4 wherein the drying accelerator comprises a catalyst containingzirconium.
 6. A composition according to claim 4 wherein the dryingaccelerator comprises a catalyst containing dibutyl tin dilaurate.
 7. Amethod for coating a golf ball with a clear polyurethane coatingcomprising the steps of: (i) providing a golf ball that is capable ofbeing coated with a clear polyurethane coating; (ii) spraying the ballwith a clear polyurethane coating mixture according to claims 4, 5, or6. (iii) moving the ball into a heated oven; (iv) allowing the ball toremain in the heated oven for a period of time sufficient to dry thecoating.
 8. The method according to claim 7 wherein the golf ball isplaced on a spindle on a chain that carries the golf ball past paintspray guns, and after being sprayed, the ball is moved along on thechain into a heated oven.